The present invention relates to a gasoline direct injection engine, and more particularly, to an engine in which intake air flow is turbulence is increased so as to increase fuel economy and decrease an amount of noxious exhaust gas during cold start.
Generally, a gasoline direct-injection and spark-ignited engine (hereinafter referred to as a DISI engine) is an engine that has advantages of both a gasoline engine and a diesel engine. In the DISI engine, fuel is directly injected into a combustion chamber.
In the DISI engine, intake flow is a very important factor in determining engine efficiency. The intake flow is determined by the shape of the intake ports, the combustion chamber, and the pistons. Research on intake flow characteristics has continuously been undertaken to prevent wall flow of the intake air and to make the intake air mix with the fuel in a short time period.
Various such engines are described in the art. For example, the DISI engine disclosed in Japanese patent publication number 4-166612, has a bowl formed in an upper surface of the piston. The bowl extends from a position under the spark plug to a position under the fuel injector. The bowl is substantially spherical, and a fuel guide groove is formed proximate to the bowl under the spark plug. Fuel injected from the fuel injector collides with a bottom surface of the bowl and moves along the fuel guide groove. Then, the injected fuel concentrates around the spark plug so that ignitability of the fuel increases.
In another example, Korean patent publication number 1997-703481 discloses a DISI engine with a bowl again formed on an upper surface of the piston. A turbulent flow is generated to some extent when fuel passes from a lower portion of a cylinder head to an upper portion of the piston, and then from the upper portion of the piston to the lower portion of the cylinder head.
However, in the above DISI engines, as in the prior art in general, the turbulence of the flow is relatively low such that it is difficult to generate a uniformly diffused air-fuel mixture. Furthermore, because a majority of the injected fuel collides with the surface of a bowl, it takes a relatively long time for the fuel to vaporize. Therefore, the late-vaporized fuel burns late so that it is imperfectly burned. As a result, soot and hydrocarbon emissions increase. In particular, while the piston is not sufficiently heated, an amount of emissions becomes very large.
In a preferred embodiment of the present invention, a combustion chamber is formed between a lower surface of a cylinder head and an upper surface of a piston. An intake valve and an exhaust valve, respectively, are disposed in an intake port and an exhaust port. These ports are respectively disposed on each side of the cylinder head. A spark plug is disposed in the cylinder head. A fuel injector directly injects fuel into the combustion chamber. Preferably, the combustion chamber is formed between the lower surface of the cylinder head and the upper surface of the piston. The lower surface of the cylinder head includes a first intake-valve-side slanted surface and a first exhaust-valve-side slanted surface. The upper surface of the piston includes a second intake-valve-side slanted surface corresponding to the first intake-valve-side slanted surface and a second exhaust-valve-side slanted surface corresponding to the first exhaust-valve-side slanted surface. Also, a bowl is formed in the upper surface of the piston. The bowl preferably extends from the second exhaust-valve-side slanted surface to the second intake-valve-side slanted surface. The depth of the bowl increases on approach to the second intake-valve-side slanted surface.
In a further preferred embodiment the direct-injection spark-ignited engine of the present invention further comprises a wall disposed in the intake port. The wall divides the intake port into an upper passageway and a lower passageway. A valve, coupled to an inlet portion of the lower passageway, selectively opens and closes the lower passageway.
It is also preferable that an intake-valve-sided ramp of the bowl is substantially vertical. More preferably, the bowl has a substantially trapezoidal shape seen from above, and a width of the exhaust-valve-side portion of the bowl is greater than a width of the intake-valve-side portion of the bowl. It is further preferred that a bottom surface of the bowl includes an upward projection part near a center position of the bowl.